This invention relates to a membrane filter for separating different molecular weight materials contained in a common solution.
Ultra-filtration is a well-known process for separating high molecular weight materials from other lower molecular weight materials in a common solution. The process involves applying a pressurized solution against a semipermeable membrane through which a portion of the feed solution permeates. Generally, the semipermeable membrane has a pore size selected to allow the passage of the permeate solution containing lower molecular weight materials at high rates while retaining the high molecular weight materials in the remaining feed solution. By the use of appropriate membranes, the larger molecules are effectively concentrated in the feed solution. The process has been applied to concentrate and/or purify proteins, enzymes, etc. in solution, but the process is especially useful in the production of food, for example, to recover protein from solutions such as whey.
A requirement for applying ultra-filtration in food production is that the filter must be easily disassembled for cleaning the membranes and the surfaces between them. Heretofore, when such filter stacks were disassembled, the membranes were often scored or otherwise damaged and upon reassembly leaks would often occur because of the difficulty of restoring the membranes in the exact positions in which they were originally interfaced with the frame or gasket that separated them. Moreover, known constructions for solving this problem were unsatisfactory because they resulted in high manufacturing cost and they usually caused other problems such as membrane rupture due to excessive distension of the membranes when subjected to the relatively high pressures used in ultra-filtration.